Tuning fork



Aug. 1,'1961 T. B. GIBBS TUNING'FORK Filed 00'0. 23, 1958 United States Patent C) 2,994,241 TUNNG FORK Thomas 'B. Gibbs, Lake Delavau, Wis., assignor to Gibbs Manufacturing & Research Corporation, a corporation of Wisconsin Filed Oct. 23, 1958, Ser. No. 769,233 2 Claims. (Cl. 84-409) This invention relates to a vibratory device or tuning fork and particularly to a tuning fork for low power, electrically driven use.

The usual tuning fork, used for musical and certain control purposes, is generally Uchaped in configuration and has two legs of relatively heavy bar-like stock. The base of the U is a heavy enlarged portion from which a supporting member extends. The thickened Ibase portion of the U has the effect of damping the vibrations of the legs or tines of the fork, and increasing the power required to keep the fork vibrating. This renders the usual tuning fork unsuitable for electrically driven use where the electrical power rating is an important factor. The relatively great thickness of the tines or legs of the fork require that the legs be quite long in order to achieve low frequency vibrations. This is undesirable where mounting space for the fork is a consideration.

A principal object of the present invention is the provision of a novel tuning fork of thin sheet stock having extremely low losses and a relatively small size at low frequencies.

One feature of the invention is the provision of a vibratory device comprising an elongated body of resilient sheet material formed into a generally U-shaped configuration. Another feature is that the device is of substantially uniform thickness and has a width which is several times 4its thickness.

A further feature is the provision of means for mounting the body of sheet material, as an ear extending outwardly from the base of the U.

Still another feature is the provision of means for tuning the device as a tuning member carried at the end of the leg of the U and movable longitudinally thereof.

And a further feature is the method of making a vibratory device, comprising cutting an elongated element of sheet material and forming the element into a generally U-shaped coniiguration.

Further features and advantages of the invention will readily be apparent from the following specification, and from the drawings, in which:

FIGURE l is a diagrammatic illustration of a thin sheet element and its principal mode of vibration;

FIGURE 2 is a diagrammatic illustration of a thin sheet element similar to FIGURE l, formed into a U-shaped configuration and indicating its principal mode of vibration;

FIGURE 3 is a plan view of a blank from which a tuning fork embodying the invention is formed;

FIGURE 4 is an elevational view of a tuning fork embodying the invention;

FIGURE 5 is an elevational view taken at right angles to FIGURE 4; and

FIGURE 6 is a fragmentary detail view illustrating means for adjusting the frequency of the fork.

An unconstrained or free body 10 of elastic or resilient material has a principal mode of vibration as illustrated by curve 11 in FIGURE 1 of the drawings. The vibrating element 10 may be a strip of a suitable thin material, as a steel alloy. The principal mode of vibration has nodal points 10a and 10b, spaced one quarter of the length of the element from the ends, and points of maximum amplitude, indicated at 11a, 11b and 11c, occuring at the ends 10c yand 10d and at the midpoint 10e of the element. Although there are often minor vibrations in other modes Patented Aug. 1, 1961 ICC and at harmonic frequencies, it is the principal mode or fundamental frequency of vibration with which the present discussion is concerned.

When the thin ilat vibratory element of FIGURE l is formed into a U-shaped configuration, as in the customary tuning fork, the principal mode of vibration is modified as illustrated in FIGURE 2. In this figure, the vibratory member 12 has elongated parallel legs 13 and 14 joined by a curved, and generally semi-circular, base portion 15. The vibrational nodes 12a and 12b are moved toward the relatively rigid base portion 15, with the entire legs 13 and 14 vibrating as a single segment. The free ends of the legs 13 and 14 have a maximum amplitude of vibration 16a and 16h, while the center of base portion 15 also vibrates, but to a much lesser extent, as indicated at 16C.

With the normal tuning fork where the base portion joining the legs from the fork is solid, the vibrations of the base portion are practically eliminated, and the legs of the tuning fork Aact as single bars fixed at one end. The restriction of the vibration in the central or base portion of the fork has a damping effect on the vibration of the legs, requiring substantial power to keep the fork vibrating. In the fork of FIGURE 2, the central portion of the body is not constrained or unduly rigidied and the vibration of the device is more analogous to the vibration of a at bar as `illustrated in FIGURE 1. The eliminations of rigidity in the base portion of the U reduces the power requirements for driving the fork.

In accordance with the invention, a vibratory device or tuning fork may be formed from a steel alloy having the proper elastic characteristics for Athe particular frequency and operating conditions of the fork. The main body 20 of the blank (FIGURE 3) is generally rectangular in configuration with the length related to the frequency of operation and a width which may be determined by desired physical characteristics, including necessary strength of the fork. (The width has relatively little effect on the frequency.)

Extending outwardly from the center portion of the blank 20 are a pair of integral mounting portions or ears 21 and 22, with ends 21a and 22a which are enlarged and provided with openings 2lb and 22h to receive a screw, bolt or other mounting device. The mounting portions 21 and 22 are made as narrow as possible depending upon the strength required for mounting the fork, to reduce objectionable effects on the vibration of the base portion, as will appear.

The blank 20 is formed into a U-shaped configuration as illustrated in FIGURE 4, with leg portions 24 and 25 extending generally parallel with each other throughout substantially their entire length. The central portion 26 of the blank forms lan integral base for the U-sh-aped fork, having a generally semi-circular configuration. The mounting ears 21 and 22 are centrally located with respect to the mid or base portion 26 of the fork and are preferably left extending straight out from the edges of the base portion. This, together with the reduced width of the ear portions minimizes the damping etfect of the supporting meansl on the central section 26 of the fork. The enlarged portions 21a and 22a at the ends of portions 21 and 22 may be formed downwardly as shown in FIGURES 4 and 5, generally at right angles to the portions 21 and 22, or in any other suitable direction, to facilitate mounting of the fork.

As the blank 20, from which the tuning fork is formed, is preferably stamped from a sheet or strip of stock material, and the normal production stamping operation does not have a very high degree of accuracy, provision is made for easily adjusting the frequency of the fork. In FIGURE 6, the end portions 24a and 25a of the legs 2.4 and 25 are formed outwardly from the major portion of the legs, at generally a right angle. These end por tions or tabs are drilled and tapped to receive two threaded adjusting screws 27 and 28 which have asignicant mass relative to the mass of the legs 24 and 25 and may be adjusted in position longitudinally of the legs to control the resonant frequency of the fork.

The tuning fork described herein is suitable for general purpose tuning fork applications.

While I have shown and dcribed centain embodiments of my invention, it is to be understood that it is capable of many modications. Changes, therefore, in the construction and arrangement may be made without departing from the spirit and scope of the invention as disclosed inthe appended claims.

I claim:

l. A vibratory device, comprising: an elongated body of resilient sheet material of generally U-shaped configuration; and a mounting ear extending outwardly and laterally from the base of said U.

2. A vibratory device, comprising: an elongated body of resilient sheet material of substantially uniform thickness throughout its length and of U-shaped coniiguration in a plane generally at right angles to the plane of the sheet material; and a pair of mounting ears extending outwardly and laterally from said elongated body at the base of said U.

References Cited in the le of this patent UNITED STATES PATENTS 329,090 Segrove Oct. 27, 1885 375,654 Segrove Dec. 27, 1887 483,513 Fuller Sept. 27, 1892 2,489,048 Rinehart Nov. 22, 1949 2,522,302 Roth Sept. 12, 1950 2,616,218 Brown Nov. 4, 1952 

